When preparing OLED devices usually printing techniques like inkjet printing, roll to roll printing, slot dye coating or gravure printing are used to apply the active layer. Based on the low solubility of most of the present organic compounds useful as emitting materials and/or charge transporting materials, these techniques need the use of solvents in high amounts.
In order to improve the film forming ability and the rheology, binding agents can be used. These additives are especially needed with regard to light emitting materials and/or charge transporting materials having small molecular weight or polymeric compounds having a low molecular weight.
The document WO 2009/109273 describes compositions comprising special solvents in order to achieve specific viscosity. Conventional compositions for printing applications like ink jet printing, flexographic or gravure printing need additives to increase ink viscosity and improve film formation.
The prior art provides compositions being useful in order to process low molecular weight organic light emitting and charge transporting materials. However, it is a permanent desire to improve the performance of the OLED layer, such as efficiency, life time and sensitivity regarding oxidation or water.
In addition thereto, the formulation should enable a low-cost and easy printing process. The printing process should allow a high quality printing at high speed.
It is therefore desirable to have improved formulations comprising an OSC that are suitable for the preparation of OE devices, especially thin film transistors, diodes, OLED displays and OPV cells, which allow the manufacture of high efficient OE devices having a high performance, a long lifetime and a low sensitivity against water or oxidation. One aim of the present invention is to provide such improved formulations. Another aim is to provide improved methods of preparing an OE device from such formulations. Another aim is to provide improved OE devices obtained from such formulations and methods. Further aims are immediately evident to the person skilled in the art from the following description.
Surprisingly it has been found that these aims can be achieved, and the above-mentioned problems can be solved, by providing methods, materials and devices as claimed in the present invention, especially by providing a process for preparing an OE device using a formulation of the present invention.
Furthermore, the document WO 2009/109273 describes compositions comprising special solvents in order to achieve specific viscosity.